Afterpulse measurement of JUNO 20‑inch PMTs

In this study,we present the large photomultiplier tube(PMT)afterpulse measurement results obtained from the Jiangmen underground neutrino observatory(JUNO)experiment.A total of 11 dynode-PMTs(R12860)from the Hamamatsu company(Hamamatsu Photonics K.K.(HPK))and 150 micro-channel plate PMTs(MCP-PMTs,GDB-6201)from the NNVT company(North Night Vision Technology Co.,Ltd.(NNVT))were tested.Subsequently,an afterpulse model was built according to the afterpulse time distribution and the probability of occurrence for these two types of PMTs.The average ratio of the total afterpulse charge with a delay between 0.5μs and 20μs to the primary pulse charge is∼5.7%(13.2%)for the tested MCPPMTs(dynode-PMTs).The JUNO experiment will deploy 20,01220-inch PMTs;this study will benefit detector simulation,event reconstruction,and data analysis regarding the JUNO experiment.

Study of the front-end signal for the 3-inch PMTs instrumentation in JUNO

A total of 25,6003-inch PMTs will be installed in Jiangmen Underground Neutrino Observatory(JUNO)to achieve more precise energy calibration and to extend the physics detection potential.Performances of all bare PMTs have been characterized and these PMTs are being instrumented with the high voltage divider,underwater front-end cable,and connector.In this paper,we present a dedicated study on signal quality at different stages of the instrumentation.An optimized high voltage ratio was confirmed andfinalized which improved the PMT transit time spread by 25%.The signal charge was attenuated by 22.5%(13.0%)in the 10 m(5 m)cable and it required the addition of 45 V(23 V)to compensate for the loss of PMT gain.There was a 1%overshoot following the PMT signal and no sign of reflection in the connector.A group of 163-inch PMTs with the full instrumentation was installed in the JUNO prototype detector together with a few 8-inch and 20-inch PMTs,which showed good stability and demonstrated a photon detection system with multiple types of PMTs.

Thermal management for the underwater frontend and readout electronics of JUNO 20‑inch PMTs

Background The Jiangmen underground neutrino observatory(JUNO)is a new generation of long-term operation neutrino experimental platform under construction in Jiangmen,Guangdong province of southern China.The underwater frontend and readout electronics(F&R electronics)are placed nearby the 20-inch PMTs and readout current signals from three PMTs.The electronics are sealed in a stainless-steel underwater box to keep them dry,and temperature control of the electronics plays a significant role in their reliability.Methods A conductive cooling structure based on the passive cooling method is designed for the 20-inch PMT F&R electronics.Both numerical simulation and experimental tests were performed to evaluate the cooling structures'thermal performance.Results The results show that the case temperature of the respective chip for 20-inch PMT F&R electronics is less than 30℃in ambient still water.Conclusion The case temperature of the respective chip meets the strict temperature requirement for the F&R electronics.The JUNO collaboration has adopted this cooling structure for the 20-inch PMT readout electronics.

PMT overshoot study for the JUNO prototype detector

The quality of PMT signals is crucial for large-size and high-precision neutrino experiments, but most of these experiments are affected by the overshoot of PMT signals from the positive HV-single cable scheme. Overshoot affects the trigger, dead time and charge measurement from a detector. For the JUNO prototype detector, we have performed a detailed study and calculation on PMT signal overshoot to control the ratio of overshoot to signal amplitude to;%, with no effect on other PMT parameters.

Characterization of 3-inch photomultiplier tubes for the JUNO central detector

Background Jiangmen Underground Neutrino Observation(JUNO)is one of the largest experimental facilities for neutrino detecting.As its main structure,the central detector contains 20 kiloton liquid scintillator filled in an acrylic shell,and there are 18,00020-inch photomultiplier tubes(PMTs)and 25,0003-inch PMTs covering the shell.Purpose As an independent photon detection system,3-inch PMTs have been required to have excellent resolution for the single photoelectron detection,high quantum efficiency,small transit time spread and low dark noise rate.Methods Two kinds of 3-inch PMTs from HZC Photonics and Hamamatsu have been investigated as candidates.A dedicated test system for 3-inch PMTs has been designed,and various characterization parameters have been studied.Conclusion The preliminary results show these PMTs can meet the requirements of JUNO.

Double calorimetry system in JUNO

Purpose Energy resolution is the key of the reactor antineutrino spectrum measurement,for the determination of the neutrino mass hierarchy.The control of the systematics of the energy response is a challenge to the large liquid scintillator experiment such as JUNO.Methods A small-PMT system was proposed to work with the large-PMT system as a double calorimetry.The individual 3-inch PMT receives mostly single photoelectrons,which provides a unique way to calibrate the energy response of the 20-inch PMT system by a photon-counting technology.Results JUNO has signed a contract with the HZC Company in May 2017 and is going to install 25,0003-inch PMTs in the central detector.The performances of HZC’s PMT samples can meet the requirements of JUNO.The mass production and testing of PMTs are in preparation,and the R&D of the readout electronics and the underwater box is ongoing.Conclusions The double calorimetry system was approved by JUNO.The system is under construction and is expected to be in operation in 2020.